Zinc foliar application may alleviate drought stress in wheat species through physiological changes

Drought is the greatest threat to food security in the climate change scenario, which affects crop plants' growth and development by disturbing the plant's physiological and biochemical processes. Zinc (Zn) is an essential micronutrient in many metabolic processes and may improve plant tolerance to water deficit conditions besides its nutritional value. This study investigated the reaction of several wheat species with different ploidy levels to foliar Zn application under water stress. Water stress significantly reduced grain yield (GY), leaf relative water contents (RWC), chlorophyll (Chla and Chlb), and carotenoid (Car) contents. Water stress also impacted several other physiological characteristics by increasing leaf hydrogen peroxide (HP), free proline (Prl), malondialdehyde (MDA) contents, soluble protein (PC), sodium content (Na+), and antioxidant enzymes, including peroxidase (Pox), ascorbate peroxidase (Aes) and catalase (Cat). Remarkably, the Zn application alleviated yield reduction caused by water stress. Moreover, the Zn application increased grains' Zn, potassium content (K+), and K+/Na+ ratio, RWC, Chl, Car contents, Pox, Aes, and Cat activities while significantly reducing MDA, HP, and Na+ contents compared with the control treatment. Pox, Aes, and Cat activities increased to higher concentrations in 6x and 4x than in 2x, indicating that the 6x and 4x species responded better to water stress. Wild and landrace varieties of 4x, such as T. dicoccum, T. ispahanicum, and T. dicoccoides, showed better water stress tolerance than the landrace varieties of 2x and 6x species. These species may be a valuable genetic source for improving modern bread and durum wheat to water stress.